Bug 2001 - Removing code that deletes flow state when a node is removed.

This patch ensures the TransactionCommitFailedException is not being caused.
We let the MD-SAL deal with clearing state and bringing it back when the node
is removed and added back.

Change-Id: Id743b9bfb83e4424f239e05dc0e731fc818f6468
Signed-off-by: Srini Seetharaman <srini.seetharaman@gmail.com>